Methyl 3-(4-fluorophenyl)-1-methyl-1,2,3,3a,4,9b-hexahydrochromeno[4,3-b]pyrrole-3a-carboxylate

In the title compound, C20H20FNO3, the pyrrolidine and benzopyran rings adopt half chair and twisted half chair conformations, respectively. The carboxylate group is almost perpendicular to the pyran ring [89.4 (1)°].

In the title compound, C 20 H 20 FNO 3 , the pyrrolidine and benzopyran rings adopt half chair and twisted half chair conformations, respectively. The carboxylate group is almost perpendicular to the pyran ring [89.4 (1) ].
The molecular conformation is stabilizaed by two weak C-H···N and C-H···O intramolecular interactions, Table 1. The crystal packing is stabilized by van der Waals forces.

Experimental
A mixture of (E)-methyl2-((2-formylphenoxy) methyl)-3-(4-fluorophenyl)acrylate(2 mmol) and sarcosine (2 mmol) in acetonitrile (8 ml) was refluxed for 5h. After the completion of the reaction mixture was concentrated and the resulting crude mass was diluted with water (15 ml). The combined organic layer was washed with brine (2x10ml) and dried over anhydrous Na 2 SO 4. The organic layer was concentrated and purified by column chromatographyon silica gel (Acme 100-200 mesh), using ethyl acetate-hexanes (1:9) to afford the pure title of the compound as a colourless solid in 65% yield.

Refinement
The H atoms were positioned geometrically and were treated as riding on their parent C atoms, with aromatic C-H = 0.93Å , methyl C-H = 0.96Å and methylene C-H = 0.97Å and with U iso = 1.5U eq (C) for methyl H and 1.2U eq (C) for the remaining H atoms.
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.